The present invention relates to apparatus for measuring injection speed in an injection molding machine, such as a die casting machine or a plastic molding machine.
It has been known that, in an injection molding machine, variation in plunger injection velocity, injection pressure, die temperature or the like gives a considerable influences on the resultant products. However, apparatus for quickly and properly measuring these quantities have rarely been used. An example of a system for measuring plunger injection velocity is disclosed in Japanese patent application No. 2689/1973. In this system, a photo electric switch is associated with a light intercepting member fixed to a plunger, and period pulses are counted by a counter while a gate of a mold is open by the interception of light, and the plunger injection velocity is computed in accordance with the number of pulses received and counted by the counter.
This system has the following disadvantages.
(1) The photosensitive element or the light source are subject to contamination with plunger lubricant, mist of the mold releasing agent, and backflow (leakage of the molten metal through a small gap formed between the plunger and a plunger sleeve caused by thermal expansion thereof) of the mold material such as aluminum, and when the light path is interrupted the operation of the photoelectric switch becomes erroneous.
(2) When the light intercepting member such as a flag is rotated, it may hit the photosensitive element or the light source to cause breakage thereof. Mounting the light intercepting member in a way in which the rotation is avoided necessitates overall modification of the machine.